The present invention is directed to a chair for dental patients comprising a chair base or substructure containing a support frame, a chair superstructure containing a seat having a seat frame, a back rest and an arrangement for pivotally hinging the back rest to the seat. In addition, the chair includes a displacement means which moves the chair frame on the support frame in a straight line manner between a first position and a second extended position with a control arrangement which controls inclination of the back rest as the seat moves between the first and second position by holding the back rest in an upright position when the seat is in a first position and tilting the back rest as the seat moves toward the second position and finally a tilting arrangement for tilting the seat as it moves from the first toward the second position.
A chair for a dental patient which has an arrangement for tilting the seat as it moves between a first position and an extended position as well as for tilting the back rest from a vertical position to an inclined position is disclosed in British patent specification No. 1,434,307 which is based on the application resulting in German Pat. No. 2,226,572. In the arrangement of these references, two parallel extending guide rods are secured on a seat frame and slidably receive sleeves which are connected to each other by a cross member and are secured to a support frame of the substructure of the device by a pivotable arrangement. In addition, the seat frame and the support frame have a roller and track arrangement so that as the seat moves between a first and second position, the seat is tilted. The back rest is pivoted to the seat and the chair arrangement includes a means for pivoting the back rest from an upright position to an inclined position as the seat moves between the first and second displaced positions. Thus, when the seat is moved from a first position with the back rest in an upright position, toward the second position, not only is the back rest tilted or inclined, but the seat itself with the corresponding foot end will be tilted upward. When the motion is reversed, the front end with the foot rest will be tilted downward and the back rest will be raised to the upright position.
To induce the guidance of the back rest during motion of the seat, a rigid connecting rod designed as an arm rest is pivotally connected to the back rest and on the other hand to the support frame.
In order to accommodate the demand for better accessibility to the patient chair, particularly when entering and departing the chair, it has already been proposed to eliminate the arm rest at the entry and departure side of the chair or to construct it so that it can be pivotally mounted and swung out of the way during entry. Such a construction which has only a single side arm rest or which has the pivotal arm rest on the other side raises problems with proper power transmission between the back rest and the support frame. If one wishes to achieve a sufficient stability, then among other things, a very involved, torsion-proof support frame for the seat and the back rest must be provided.